1. Field of the Invention
The present invention relates to a polymer electrolyte fuel cell and a stack therefor, and a method of manufacturing the same. More particularly, the present invention relates to a polymer electrolyte fuel cell and a stack therefor, and a method of manufacturing the same, wherein the stack for the fuel cell is made by attaching thermoplastic elastomer parts to one another to maintain the insulation and sealing of separator plates so that the stack is simplified in structure and reduced in weight, thereby simplifying processes and reducing costs upon manufacture thereof.
2. Description of the Related Art
Since a polymer electrolyte fuel cell (PEFC) has advantages in that it has high current density and low operating temperature and also has no risk of corrosion and electrolyte loss, PEFC has been developed as military or spacecraft power sources. There have been actively conducted studies on applications thereof to automobile or mobile power sources using features by which output density is high and devices can be simplified and formed into modules.
As for the basic structure of the polymer electrolyte fuel cell, the polymer electrolyte fuel cell comprises porous air and fuel electrodes coated with platinum, which is a noble metal catalyst, existing at both ends with respect to a polymer electrolyte membrane, and cell frames for supporting the electrodes and defining gas passages.
Hydrogen acting as fuel is introduced toward the fuel electrode and oxygen or air acting as oxidant is introduced toward the air electrode. Electrical energy is then generated through electrochemical oxidation of the fuel gas and electrochemical reduction of the oxidant. That is, the reduction reaction of the oxygen and the oxidation reaction of the hydrogen occur at the air and fuel electrodes, respectively, resulting in generation of electricity and water.
Thus, in view of the entire cell, hydrogen and oxygen are introduced into the cell and electricity, heat and water are discharged.
Methods of improving the output of a cell include a method of increasing the area of a cell, and a method of connecting a plurality of cells to one another. The increase in the area of a cell causes the voltage of the cell to be constant but an output current to be increased. The connection of the plurality of cells causes an output current to be constant but the voltage of the cells to be increased.
Although each of the both methods can be performed in theory, practicable cells are manufactured by means of a method of improving cell output by appropriately increasing the area of each cell and simultaneously stacking a plurality of unit cells in consideration of the both factors.
The stacking of unit cells means that unit cells with the same size and configuration are connected to one another in series such that a fuel electrode of a first unit cell is brought into contact with an air electrode of a second unit cell. In this case, a cell frame for the fuel electrode of the first unit cell is generally formed not separately from but integrally with a cell frame for the air electrode of the second unit cell, resulting in a separator plate.
Flow passages through which gases flow are formed on both sides of the separator plate such that hydrogen flows through a flow passage on one side and oxygen flows through a flow passage on the other side.
The reaction gases are supplied to the cells from external storage containers and then into the separator plate through cell manifolds. When the reaction gases reach the respective electrodes through the separator plate, electrochemical reactions occur on surfaces of the electrodes.
At this time, hydrogen and oxygen as the reaction gases are supplied to the fuel electrode and the air electrode, respectively. The two gases should not come into direct contact with each other. If the two gases come into direct contact with each other, a combustion reaction occurs instead of an electrochemical reaction and thus electricity is not generated and only heat is generated, which leads to breakage of the cells.
To ensure that the two gases flow through the respective flow passages without mixture thereof, it is necessary to maintain sealing around the gas passages.
FIG. 1 is a view showing the structure of a conventional polymer electrolyte fuel cell. Such a polymer electrolyte fuel cell used as a power source for a fuel cell-powered automobile comprises several dozens to hundreds of serially stacked unit cells 10 consisting of bipolar separator plates 11 serving as current collectors and fuel supply passages, membrane-electrode assemblies 12 and gaskets 13 for ensuring sealing for fuel gas and cooling water; and fasteners 20 such as end plates 21, high-tension bolts 22, and nuts 23 for supporting the stacked unit cells.
However, in the structure of such a stack constructed by stacking several hundreds of unit cells, since gaskets, end plates and fasteners are used as means for maintaining sealing for gases and supporting the stack, there are problems in that the number of parts increases and mass-production thereof is difficult.